1. Field of the Invention
This invention relates to remotely controllable vehicles adapted to service and/or inspect limited access areas such as the interior of a nuclear steam generator.
2. Description of the Prior Art
A nuclear steam generator 12 of the type found in the prior art is shown in FIG. 1 of the Attached drawings, as comprising a bundle of a large number of vertically oriented U-shaped tubes 28. The tubes 28 are disposed in a lower, cylindrically shaped shell 14 of the steam generator 12, whose bottom end is associated with a radiation confining housing or channel head 16, typically of a hemi-spherical configuration as shown in FIG. 1. The channel head 16 is divided by a partition 22 into a first half typically known as a hot leg 18, and a second half typically known as a cold leg 20. High-temperature primary water from a nuclear reactor is introduced into the steam generator 12, through a primary inlet (not shown) into the hot leg 18. The primary water passes from the hot leg into the exposed openings of the plurality of U-shaped tubes 28, flows through the tubes 28 to be introduced into the cold leg 20 and, finally, exits from the steam generator 12 through a primary outlet (not shown). Opposite ends of the U-shaped tubes 28 are mounted within a tube sheet 26 in communication with the hot leg 18 and the cold leg 20, respectively. A wrapper 24 surrounds the bundle of U-shaped tubes 28.
Inlet or secondary water is introduced into the lower shell 14 to circulate about the U-shaped tubes 28, whereby pressurized steam is produced and supplied to a steam turbine (not shown). Further, the primary water circulating through the hot leg 18 and cold leg 20 of the channel head 16 is radioactive and has therein chemical contaminents. The high temperature water/steam environment within the steam generator 12 corrodes the U-shaped tubes 28 causing the rupture and the leakage of the radioactive primary water into the lower shell 14 of the nuclear steam generator 12. In the prior art, degradation and rupture of the U-shaped tubes 28 was attributed to either microscopic attack from chemical contaminents in the primary water or mechanical deformation. More recently, investigation of nuclear steam generators has indicated the presence of relatively large foreign objects such as hand tools, "C" clamps and steel blocks to be the cause of peripheral tube damage in the secondary side of nuclear steam generators. To prevent or minimize damage from such foreign objects as contaminents, routine inspections of the primary side including the tube sheet 26 and the secondary side including the peripheral surfaces of the U-shaped tubes 28 are carried out.
Inspection of the channel head 16 exposes personnel to significant radioactivity. Devices are known in the prior art that are insertable within the channel head 16 to permit inspection of the ends of the tubes 28 and the tube sheet 26, whereby exposure to personnel to radiation may be reduced. U.S. Pat. No. 4,287,655 of Gerkey et al., assigned to the assignee of this invention, discloses a machine for servicing the tube sheet 26 of the nuclear steam generator 12. The Gerkey et al. machine includes an arm pivoted to move in a plane parallel to and underneath the semicircular hole array in one-half of the tube sheet. A carriage mounted for reciprocal movement along the arm is provided with a platform which can be raised toward the tube sheet. In order to carry out selected operations on the tube sheet, various end effectors may be mounted on the platform. Due to the constraints imposed by the shape of the channel head, it is necessary that the end effectors by mounted on cantilevered arms and that the cantilevered arms be mounted at different angles on the platform in order to reach all of the holes in the array with the different end effectors. In some instances, cantilevered arms of more than one length are required for one type of end effectors in order that the desired operations can be performed at each of the holes in the array. The alignment of the end effectors causes sensor elements associated with the cantilevered arms to generate signals indicative of the position of the aligned tube holes in the channel head 16, whereby various servicing operations, e.g., drilling, may be carried out upon that tube within the aligned hole.
The following patents relate to apparatus similar to that disclosed in the Gerkey U.S. Pat. No. 4,287,655 and are, likewise, assigned to the assignee of this invention: U.S. Pat. No. 4,205,939 of Reyes; U.S. Pat. No. 4,205,940 of Golick; U.S. Pat. No. 4,216,893 of Glatthorn; U.S. Pat. No. 4,213,732 of Cooper, Jr.; and U.S. Pat. No. 4,247,974 of Golick.
U.S. Pat. No. 3,811,320 of Cowell describes apparatus controllably moved through such limited access areas as a tank or the like. The Cowell apparatus includes a vertically disposed cross-member having a track to be reciprocally driven by a motor, and a horizontally disposed cross-member likewise having a track reciprocally driven by a second motor. Each of the first and second cross-members have a pair of electromagnets for releasably attaching its cross-members to the wall of the tank. Each cross-member rides on the track of the other cross-member, so that as one cross-member is attached by its pair of electromagnets to the wall, the other cross-member is driven by its motor to the next position. Movement is achieved by first energizing the magnets of the vertically disposed cross-member and, then, driving the horizontally disposed cross-member in a horizontal direction. Thereafter, the pair of magnets of the horizontally disposed cross-member is energized and those of the vertically disposed cross-member deenergized, whereby the vertically disposed member may be moved to a different position. The apparatus may be moved in a vertical direction by reciprocally energizing the first motor and selectively energizing and deenergizing the magnets on the first and second cross-members. If both of these motors are energized while one cross beam member is locked in position by its pair of electromagnets, than the apparatus may be driven in a 45.degree. direction with respect to its cross-members. Movement of this device is stated to the controlled by computer, but the details of such control are not disclosed. Further, no means are disclosed, whereby the exact position of the servicing or sensing apparatus is ascertained.